Is Pfizer's Covid vaccine less effective than previously believed in 5- to 11-year-olds?
On Monday, a paper that suggested as much was posted on a server by researchers with the New York State Department of Health; that paper has yet to be peer-reviewed. On top of the vaccine being delayed for children under the age of 5, the news came as a major disappointment to parents. The paper suggested that there has been a rapid decline in protection after vaccination among the youngest cohort of children eligible for vaccination, dropping off more quickly than the declines seen in slightly older children aged 12 to 17.
In their study, researchers analyzed data from 852,384 fully vaccinated children aged 12 to 17 years and 365,502 children aged 5 to 11 years between Dec. 13 and Jan. 31, 2022 — the peak of the omicron surge. The analysis suggested that the vaccine's effectiveness against hospitalizations declined from 85 to 73 percent for the older children, and from 100 percent to 48 percent for 5- to 11-year-olds. Vaccine effectiveness against infection decreased from 66 percent to 51 percent for older children, and from 68 percent to 12 percent in the younger cohort.
"Our data support vaccine protection against severe disease among children 5-11 years, but suggest rapid loss of protection against infection, in the omicron variant era," the New York state researchers wrote. "Should such findings be replicated in other settings, review of the dosing schedule for children 5-11 years appears prudent."
The lower dosage of vaccine given to younger children (compared to adults) relates to differences in the human immune system, as well as in body mass. While everyone over the age of 12 receives two shots of the Pfizer vaccine 21 days apart, each dose containing 30 micrograms of vaccine, children 5 to 11 receive two doses that are 10 micrograms each — one-third the adult-dose. As the researchers stated, the dosing for children might need to be re-evaluated should these findings about vaccine effectiveness be repeated in future trials.
Still, there remains conflicting data over whether or not vaccine effectiveness is actually waning in 5- to 11-year-olds — and if the dose amount is to blame, or if it's something else.
A day after the preprint study made headlines, the Centers for Disease Control and Prevention released data suggesting the dosing isn't the issue. Instead, it was the omicron variant to blame for the perceived drop in vaccine effectiveness; unlike with other patients, vaccinations for 5- to 11-year-olds started weeks before the variant began circulating. Indeed, data from the CDC showed that two doses of the Pfizer vaccine still hold up for 5- to 11-year-olds against severe illness and hospitalization at the same rate as 12- to 17-year-olds.
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According to the CDC data, which analyzed data from 10 states from last April to January, vaccine effectiveness against hospitalizations for 5-to 11-year-olds was 74 percent; two vaccinated children were hospitalized, compared to 59 unvaccinated children. For adolescents ages 12 to 15, vaccine effectiveness against hospitalization was 92 percent; and 94 percent for teenagers between 16 and 17 years old.
Experts tell Salon the main takeaway is that vaccines work for children in preventing hospitalization and severe illness, but they're not necessarily as effective against preventing an infection despite vaccination — which is the same case for adults. Studies have shown that omicron is more transmissible and also better at evading vaccine-induced immunity; the current Pfizer vaccine was designed to protect against the original COVID-19 strain.
"So the main point here, from both studies, is that two doses of the vaccine does really well at preventing severe illness and hospitalizations," said Litjen Tan, chief strategy officer of the Immunization Action Coalition. "However, as we have seen in adults, with omicron, effectiveness against infection itself is reduced and the duration of that protection is shorter that what we saw with the original strain."
Tan noted that in the CDC data, a booster for adolescents greatly improved protection against infection.
"It is also clear from the CDC data that a booster dose significantly improves that protection (effectiveness) against infection," Tan said. "It would not surprise me if the duration of the protection is less than what we saw with the original strain, or even delta."
Dean Blumberg, chief of pediatric infectious diseases and associate professor in the Department of Pediatrics at the University of California, Davis, noted to Salon that there is a wide confidence interval — meaning the degree of certainty — with the New York data. That could be a yellow flag, he noted.
"If you look at those numbers, if you look at the number of cases of hospitalizations, for example per week, there's less than 10 per week in the vaccinated group," Blumberg said. "Even though the study involved hundreds of thousands of children, the number of hospitalizations for the 5 to 11 year olds is relatively small, and that's why the confidence intervals are so wide, so it just really it makes you wonder about the significance of it because the numbers are relatively small, especially for the hospitalization."
Blumberg his major takeaway is that more research is needed — research that is less "suggestive" and more "definitive" about decreased protection in young children.
Both Tan and Blumerg agreed that vaccinating children is still the best way to protect children against COVID-19.
"Getting vaccinated remains the best way to stay healthy and reduce the pressure on our hospitals and healthcare workers," Tan said.
Blumberg noted while children are less likely to be hospitalized and have COVID-19 in general, there has still been a significant number of children who have been infected.
"Millions of kids have been infected, and there have been thousands of hospitalizations," Blumberg said. "Although the outcomes are generally better, there still can be serious consequences of infection, and we also need to consider those children who recover and may have long COVID, and how that could really interfere with their physical activities as well as their school learning activities."
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